The development and/or manufacture of various products, such as circuit boards for a computer, frequently includes vibration testing. Such testing is needed to determine if the product can withstand vibration forces of the type expected to be encountered during use of the product.
Conventional vibration testing typically involves attaching the test object to the top surface of a shaker table or a sliptable coupled to a shaker table and then activating the shaker table for a suitable period of time. Since it is frequently desirable to vibration test an object along two or more of its axes, in the past it has been necessary to reposition the test object after each vibration test so as to align the various axes of interest of the object in selected relationship with the axis of the vibration force generated by the shaker table. The time and cost of vibration testing an object is increased significantly when the object must be repositioned for every axis along which the object is to be vibration tested.
In an attempt to minimize the time associated with repositioning an object to be vibration tested along three mutually-orthogonal axes thereof, Marshall et al. developed an apparatus for automatically repositioning a test object, as disclosed in U.S. Pat. No. 4,848,160, issued July 18, 1989. The latter apparatus comprises a cubic fixture for supporting an object to be vibration tested, a head expander positioned between the cubic fixture and a vibration source, an index assembly for raising the cubic fixture away from and lowering the cubic fixture onto the head expander, and a rotation assembly for rotating the cubic fixture about its diagonal axis when the fixture is raised above the head expander. The apparatus also includes a controller for automatically raising, rotating and lowering the cubic fixture so that vibration testing can be performed along three mutually-orthogonal axes of the test object without detaching the object or the cubic fixture on which it is supported from the vibration source during the three-test sequence.
Although the Marshall et al. apparatus functions satisfactorily when it is desired to vibration test an object along three mutually-orthogonal axes thereof, the apparatus tends to be complex, and is hence more costly than is required when it is desired to vibration test an object along axes lying in a single plane. As such, the cost of performing the latter vibration tests tends to be more involved and expensive than necessary. Additionally, the Marshall et al. apparatus is limited in that the test object must be detached from the cubic fixture and repositioned if it is desired to vibration test the object along axes other than the three mutually-orthogonal axes of the object along which vibration testing was first performed.
To overcome some of the above-listed limitations of the apparatus disclosed in U.S. Pat. No. 4,848,160 to Marshall et al., a test fixture was developed for translating a single vibration force into three equal vibration forces which extend along three mutually-orthogonal axes and for applying the forces to a test object so that each of the forces extends parallel to a corresponding-respective one of three mutually-orthogonal axes of the object, as disclosed in U.S. patent application Ser. No. 362,757, filed June 7, 1989 in the name of Philip Marshall (the '757 application). The fixture disclosed in the '757 application comprises an inclined top plate for supporting a test object in selected angular relationship relative to a shaker table or sliptable, and a base for securing the top plate to the shaker table or sliptable.
Although the fixture disclosed in the '757 application functions satisfactorily, the latter fixture permits an object to be vibration tested along only two axes lying in a given plane of the object. The test object must be detached from the fixture, repositioned, and reattached to the fixture if it is desired to vibration test the object along more than two axes in a given plane. This characteristic of the fixture of the '757 application can be limiting when it is desired to perform more than two vibration tests in a given plane of a test object without detaching the object from the support fixture to which it is attached.